The Hg(Ⅱ ), Ce(Ⅲ ) and Th(Ⅳ ) complexity were prepared by reaction of HgCl₂, Ce(NO₃)₃· 6H₂O and Th(NO₃)₄· 5H₂O metal ions with (1 mmole) in 25 mL distilled water to dissolved Captopril (25 mL of 99% CH₃OH) with molar ratio 1:2. The pH of Captopril metal ions mixtures are between ~8.0~9.0 using 5% ammonium hydroxide. The product was stirred and refluxed at 70 ℃ for 3 h. The obtained precipitates were filtered off and washed with distilled water and CH₃OH. The solid product precipitates were dried at 70 ℃ under vacuum over anhydrous calcium chloride.

The C, H and N percentage determined using Vario EL Fab. CHNS. Metal content and water percentage were determined by TG/DTG. IR data for CPA complexity were measured using infrared Bruker spectrophotometer ranged between 400~4 000 cm^-1. The conductance measurements with concentration of 10^-3 mol· L^-1 for complexity in dimethyl sulfoxide solvent measured using HACH conductivity meter model. ¹H-NMR was recorded as dimethyl sulfoxide solutions on a Bruker 600 MHz spectrometer using tetramethyl silane as the internal standard. TGA experiments were conducted using Shimadzu TGA-50H thermal analyzers. All experiments were performed using a single loose top loading platinum sample pan under N₂ atmosphere at a flow rate of 30 mL· min^-1 and a 10 ℃· min^-1 heating rate for the temperature range 25~800 ℃.

Molar conductance data of the complexity are 43, 45 and 16 μ s· cm^-1 for the Ce(Ⅲ ), Th(Ⅳ ) and Hg(Ⅱ ) CAP respectively. Based on electrolytic measurements of the Ce(Ⅲ ), and Th(Ⅳ ) complexity, NO3-anion have coordinated character and exists inside coordination sphere, while in case of Hg(Ⅱ ) complex, the Cl^- anions have uncoordinated character and didn’ t exists inside and outside coordination sphere^[11].

The main bands in the IR of the free captopril ligand and their metal complexes (Fig.2) which summarized in Table 2. The infrared data refers to involvement of carboxylic and carbonyl groups in chelation, together with water, that presented inner or outer coordination sphere of Ce(Ⅲ ) and Th(Ⅳ ). The presence of broad band’ s at 3 408 and 3 426 cm^-1 which didn’ t found in the free CPA spectrum, indicates the presence of water molecules that disappears after heating the complexes at 100 ℃. In principle the ligand can exhibit band at 3 300 cm^-1 which may be assigned to ν (OH) of carboxylic group. IR of the ligand show strong band within the region 1 742 and 1 446 cm^-1 which may be assigned to asymmetric ν (COO) and symmetric ν (COO), respectively. The band at 2 562 cm^-1 was assigned to ν (S— H)^[12], this peak remains unshifted in the spectrum of Th(Ⅳ ) and Ce(Ⅲ ) complexes.The presence of (C— S) band at 980 cm^-1 in the ligand which didn’ t changed in the Th(Ⅳ ) and Ce(Ⅲ ) complexes confirm that SH group not participate in coordination process (Fig.3). The absence of these band at 2 562 cm^-1 attributed to ν (S— H) and the decrease in vibration of (C— S refers to that SH group participate in coordination in case of Hg(Ⅱ )/CAP complex. The strongest absorption peak at 1 648 cm^-1 is due to C=O stretching vibration. This peak became weak and shifted to 1 607 and 1 593 cm^-1 show a bathochromic shift in the spectrum of complexes which suggests bonding of captopril through C=O group. The spectrum of the complexes exhibited broad band’ s at 3 400 cm^-1 that are attributed to OH of crystal water molecules. The low intensity bands at 600~400 cm^-1 are attributed to vibrations of metal— O and metal— S^[12]. Other bands observed in case of Ce(Ⅲ ) and Th(Ⅳ ) complexes at ~1 460, ~1 270, ~1 030, and ~730 cm^-1 corresponding to ν ₁, ν ₄, ν ₂ and ν ₃ vibrations agree with frequencies reported for bidentate nitrate group^[12]. Tie separation of highest frequency bands ν ₁ and ν ₄ (180~140 cm^-1) in the complexes favors bidentate character of the nitrate group^[12]. These data support a bidentate chelation of CAP with Ce(Ⅲ ) and Th(Ⅳ ) through C=O and deprotonated COOH group while for Hg(Ⅱ ), CAP acts as a bidentate ligand through C=O and deprotonated SH group molecules (Fig.3).

Fig.2(a)

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	Fig.2(a) FTIR spectrum of Hg(Ⅱ ) CAP complex

Fig.2(b)

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	Fig.2(b) FTIR spectrum of Ce(Ⅲ ) CAP complex

Fig.2(C)

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	Fig.2(C) FTIR spectrum of Th(Ⅳ ) CAP complex

Fig.3

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	Fig.3 Speculated structures of Hg(Ⅱ ), Ce(Ⅲ ) and Th(Ⅳ ) captopril complexes

Table 2

Table 2

Table 2 Infrared spectral bands and assignments of CAP complexes Compound ν (O— H) hydrated ν (SH) ν (C=O)amide ν (C=O)acid ν (M— N) ν (M— O) ν (C— S) CAP - 2 562 1 648 1 755 - - 980 Ce(Ⅲ ) 3 408 2!557 1 593 - 450 598 982 Th(Ⅳ ) 3 426 2 557 1 607 - 420 546 985 Hg(Ⅱ ) - - 1 610 1 735 - 547 916

Table 2 Infrared spectral bands and assignments of CAP complexes

The ¹H-NMR spectral analyses for CAP compound in DMSO-d₆ has a singlet sharp signal at 1.90 ppm referred to the proton of — SH, this signal not found in the spectrum of the Hg-CAP complexity due to the deprotonation of the — SH group. The non-equivalent protons of pyrrolidine ring — CH₂ protons, appear as at 2.48~2.51 ppm. The ¹H-NMR spectral analyses of the CAP ligand has a singlet sharp signal at 8.53 ppm attributed to the proton of — COOH, this signal not affected in spectrum of the Hg/CAP complexity, supported that carboxylic group not involved in the coordination. These facts confirms the coordination site of captopril which discussed above.